Haemophilus ducreyi is a Gram-negative bacterium that infects the genital epidermis in humans, causing the sexually transmitted disease (STD) 'chancroid'. This pathogen disrupts the epithelium and forms genital ulcers. Chancroid can act synergistically with other genital diseases to effect an overall rise in STDs and AIDS. This disease continues to be endemic to large parts of the world, and appears disproportionately among minority heterosexuals and in the southern US, where it may now be endemic. This proposal seeks to define the structures and functional roles of surface lipooligosaccharides (LOS) in the pathogenesis of H. ducreyi. The investigator proposes to address the relationship of LOS structures (or chemotypes) to specific phenotypic traits (adherence, invasion, etc.) that are critical in defining the molecular determinants of H. ducreyi virulence. Given these goals, the investigator defines four major aims for this proposal: Specific Aim 1 is proposed to identify and characterize novel LOS-oligosaccharide structures and biosynthetic pathways as expressed among wild-type strains of H. ducreyi and assay for functional differences in these LOS-oligosaccharide structures. Specific aim 2 is proposed to construct and characterize the structures of LOS produced by defined mutants defective in LOS biosynthesis as tools to elucidate the synthetic pathways and functional roles of LOS in adhesion and invasion mechanisms. These studies will include work on the heptosyl and galactosyl transferase mutants of strain 35000 (losA-and losB-), as well as mutants defective in sialic acid (neuA) and lipid A biosynthesis. Specific aim 3 is proposed to examine the specificity, binding affinities and valence of LOS-lectin interactions as a model for bacterial cell adhesion to human epithelial cells. The investigator proposes to identify the receptors involved in LOS binding, and to construct and test multi-valent carbohydrate ligands as biological and chemical models of the LOS-receptor interaction. Specific aim 4 is proposed to characterize key enzymes involved in the biosynthesis of LOS that contain sialic acid, such as the CMP-NeuAc synthetase and H. ducreyi sialyltransferase. The investigator hypothesizes that data obtained from these studies will allow the investigator to determine the roles of LOS in H. ducreyi infection at the molecular level. The investigator's long-term goals are directed towards understanding the basic chemistry and biology of bacterial pathogenesis, as well as to exploit this information to develop novel therapeutics such as LOS-based vaccines, carbohydrate inhibitors, and/or inhibitors targeting LOS biosynthesis.